Polymers of alpha-olefins prepared in the presence of ionic catalyst systems, as for example polypropylene prepared using a catalyst comprised of diethylaluminum chloride and a titanium trichloride, contain greater or lesser amounts of low-molecular-weight and, particularly, amorphous components which, when taken alone, are alkane soluble materials. The presence of these alkane-soluble materials in the polymers leads to difficulties during the fabrication of products therefrom and to inferior physical properties in the finished items, and hence are almost always removed in commercial processes for the production of polypropylene. Production of these components leads to an economic disability for the polymerization process as they have little usefulness and extra process steps are required to remove them from the commercial product.
In the past a number of materials and combinations thereof have been reported in the patent literature as useful additives to transition metal compound -- alkylaluminum compound catalysts to reduce the alkane-soluble fraction produced during the polymerization process. Among these additives are amines, amine oxides, ethers, organophosphites, and mixtures of organotin sulfides and amines, amine oxides or organophosphites. The mixtures containing organotin sulfides have been described as showing a greater effect on solubles reduction than either component of the mixture alone. However, such mixtures have some disadvantages which include the high cost of organotin sulfides.
In addition, it has been disclosed in U.S. Pat. No. 3,159,614 that reacting the transition metal component of these types of catalysts with hydrogen sulfide or selenide aids in producing more highly crystalline polymer when used to polymerize olefins.
Since it is generally true that slowing an alpha-olefin polymerization down produces more of the desired crystalline polymer, and that additives when their concentrations become high enough slow the polymerization, the object of the work leading to the invention taught herein is to obtain the maximum solubles reduction with the smallest effect upon rate.
Now it has been found that by using hydrogen sulfide and a sterically hindered, lower alkyl substituted, cyclic, tertiary amine, a sterically hindered, lower alkyl substituted, cyclic, amine oxide or a trihydrocarbylphosphite, as additives to titanium trichloride-alkyl-aluminum compound catalysts, systems are formed which, when used for propylene polymerization, can result in a substantial reduction of the alkane solubles while not seriously affecting the total yield of polymer. The systems taught herein (combinations of additives) can be better in solubles reduction than either additive of the combination alone. In addition, the systems taught herein can result in an improvement in solventless polymerization processes wherein the olefin is polymerized directly from the vapor or liquid phase. The catalyst systems disclosed herein may also be used for alpha-olefin polymerizations wherein supported or other types of high activity transition metal compound components are employed.